1. Field of the Invention
The present invention relates to a method for manufacturing dried sweet potato chips which are edible as a snack food and their starting sweet potato chips, in particular extremely thin sweet potato chips having a thickness on the order of 0.3 to 1 mm.
2. Prior Art
Up to now the only chip-type snack food has been widely marketed is the potato chip made from sliced potato. Recently, however, attempts have been made to market sweet potato chips as a snack food. For instance, in Japanese Patent Un-examined Publication (hereinafter referred to as "J. P. KOKAI") No. Sho 55-15701, there is disclosed a method for producing sweet potato chips which comprises slicing sweet potatoes to a thickness of about 2 mm, heat-treating the sliced sweet potato, then freezing it, and frying the sliced and frozen sweet potato as such or after thawing. In addition, methods in which sweet potatoes are sliced to a thickness of about 2 mm (J. P. KOKAI No. Sho 59-31668) or a thickness on the order of 0.5 to 5 mm (J. P. KOKAI No. Sho 60-172269) and then fried to obtain sweet potato chips are also known. Moreover, there have also been known a method for manufacturing sweet potato chips which comprises slicing sweet potatoes to a thickness on the order of 3 to 4 mm, frying the sliced sweet potato to heat up the same and then freezing them (see J. P. KOKAI No. Sho 62-91159) and a method for producing sweet potato chips which comprises slicing sweet potatoes, immersing the sliced sweet potato in a solution of, for instance, a carbonate, and then frying the same (see J. P. KOKAI No. Sho 62-91160).
In general, the most suitable cooking temperature for bringing out the sweetness specific to sweet potato ranges from 60.degree. to 80.degree. C. However, in the aforesaid methods, raw sweet potatoes are first sliced and then subjected to a heat treatment such as a frying and, therefore, these treatments rapidly pass through such temperature range required for developing optimum sweetness of sweet potato. This results in the formation of sweet potato chips having insufficient sweetness. Moreover, to sufficiently develop the sweetness of the sweet potato it is considered that the sweet potato should first be sufficiently steamed and then sliced, but it is difficult to slice steamed sweet potato to a desired thinness and thus sweet potato chips having a desired thickness on the order of 1 mm or less cannot be obtained.